Morphology and N2 permeability of multi-wall carbon nanotube--Teflon membranes.

We prepared buckypapers with surface densities in the 1.13-5.66 mg x cm(-2) range by filtering multi-wall carbon nanotube (MWCNT) suspensions in acetyl-acetone (acac) and dimethylformamide (DMF) through 0.45 microm nylon filters. Filtration curves were evaluated using the Carman equation. The average resistance of the filter itself was found to be Rm = 3.79 x 10(10) m(-1) for acac and 8.49 x 10(10) m(-1) for DMF The specific resistance a of the filter cakes decreased with increasing film surface density from 16.1 x 10(12) m x kg(-1) (for the 1.13 mg x cm(-2) film from DMF) to 4.38 x 10(12) m x kg(-1) (for the 5.66 mg x cm(-2) film from DMF). The effective diffusivity of N2 at 298 K and a pressure difference of 10 mbar was also determined for all membranes and found to fall into the 1.14 x 10(-9)-3.74 x 10(-9) m2 x s(-1) range. Both the porosity and the tortuosity of buckypapers increased with their thickness. An approx. 5 microm thick Teflon (PTFE) coating was applied to the MWCNT membranes by pulsed laser deposition. The gas permeability of the MWCNT-PTFE membranes matches that of the uncoated nanotube films. This observation is an agreement with our SEM and AFM data on porous coating morphology.